Method and apparatus for electrical precipitation



DEUTSCH July 16, 1935 METHOD AND APPARATUS FOR ELECTRICAL PRECIPITATION Filed May 11, 1932' 4 Sheets-Sheetl INVENTORZ ATTORNEYS July 16, 1935. g T 2,008,246

METHOD AND APPARATUS FOR ELECTRICAL PRECIPITATION Filed May 11, 1932 4 Sheets-Sheet 2 I INVENTOR. -2 41W,

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A ORNEYS/ July 16, 1935. w. DEUTSCH METHOD AND APPARATUS FOR ELECTRICAL PRECIBITA'IION Filed May 11, 1932 4 Sheets-Sheet 3 FIG H INVENTOR:

u y 16, 1935. w. DE TSCH 2,008,246

METHOD AND APPARATUS FOR ELECTRICAL PRECIPITATION Filed May 11, 1932 4 Sheets-Sheet 4 INVENTOR:

ATTORNEYS.

Patented July 16, .1935

PATENT OFFICE METHOD AND APPARATUS FOR ELEG- raIcAL rnncrrrrxrron Walther penises, Frankfort-dn-the-Main; Germany, assignor to International Precipitation Company, Los Angela, Caliil, a corporation of California Application May ll, 1932, Serial No. 610,682 In-Germany May 22, 1931 6 Claims. (01. 183-7) This invention relates to the electrical'precipitation of suspended particles from gases.

The principal object of .the invention is to provide a novel method and apparatus adapted to efiect highlyeincient and economical cleaning of gases by electrical action. r

In electrical gas cleaning methods now commonly employed, the gas is passed between discharge electrodes of small surface and sharp surface curvature, such as wires, small diameter rods, members having sharp edges orcorners, serrated strips or the-like, and collecting electrodes of extended area, formed either as plane surfaces or as surfaces of relatively small curvature, such as 15 plates, screens, or pipes of relatively large diameter. A suitable potential diiference is maintained between said electrodes, and such potential difference is ordinarily unidirectional, the discharge electrodes being generally maintained at nega- 20 tive polarity and the collecting electrodes at positive polarity'with respect to one another. In such apparatus, the electrical potential between the electrodes is suificiently high to produce corona or silent discharge at the'surfaces of and imme- 25 diately adjacent the discharge electrodes, resulting in the formation of ions in this'region, prin- .cipallyby impact'ionization, and the ions thus formed attachthemselves to the suspended particles. The particles thus charged are then driven by the electrical field toward and upon the sur= faces of the collecting electrodes. It will be seen, therefore, that the same electrical field is used for eifecting ionization and charging of the suspended particles and for causing precipitation of the charged particles, andthis has resulted in certain disadvantages, due to the fact that the optimum conditions of the electrical field for ionization and charging purposes are determined 40 by somewhat different considerations than the precipitation purposes. In order to provide sufilcient corona discharge to produce the desired amount of ionization, it is necessary to mainr tain a relatively high potential between the elec.

trodes, for example, on the order of 30,000 to 50,000 volts, and this, in turn, requires that the electrodes be placed relatively far apart from one another in order to prevent arcing or disruptive discharge between electrodes of this type.

" While the electrical field intensity in the region of the corona or brush discharge is relatively great,

the intensity decreases toward the collecting elec-- trode, and it is impossible to nr aint'ain the electric field intensity above a certain limiting value in the major portion of -the region between the,

optimum conditions for the electrical field for installation and electrodes. This limits" the electrical force tend-- ing to drive the charged particles toward the collecting electrode. Therefore, due to the limited electrical force available for precipitation purposes, and also to the relatively large distance between the electrodes, the time required for movement of any charged particle'from a position out in the gas stream tothe surface of the collecting electrode is relatively great, which not onlyincreases the size of apparatus required but also affords considerable opportunity for the particles to lose their electricalcharge or to combine with oppositely chargedparticles, and thus inhibit precipitation thereof. Furthermore, this makes it necessary to employ unidirectional electric power, for if alternating current is used, the duration of each half cycle is not. sufficient to cause complete precipitation of a"1arge proportion of the charged particles, and the particles are therefore simply driven back and forth in the gas stream without being precipitated.

A further object of'the invention, therefore, is

to provide a method and apparatus in which the electrical field employed for precipitation of the charged particles is separate from the electrical 5 field employed for ionization and charging of the particles. a

- A further object of the invention is to permit a maximum electrical field intensity to be maintained throughout all portions of the precipitat- 3 ing field, and also to provide a relatively small -spacing between the oppositely charged precipitating electrodes, thus providing a maximum precipitating force and a minimum averagelength of path for precipitation of the particles, both of which factors minimize. the'time required for complete precipitation and also minimize the opportunity for recombination and discharging of the charged particles.

A further object of the invention is to provide 40 a method andapparatus in which alternating current electrical fields maybe efliciently and economically utilized, both for charging the particles and for precipitation thereof, thus eliminating the necessity of providing rectifying apparatus and reducing both theginitial cost of the the cost of maintenance and operation. p

A further object of the invention, in some cases,

is to simplify the construction and bring the chargingfield as close-as possible to the precipitating field, by causing the electrical discharge to take place from the forward edges or portions of the: precipitating field electrodes, while the major portion of these precipitating field electrodes,

a separate group of oppositely charged electrodes,

or between discharging portions at the forward ends of the precipitating electrodes and an auxiliary electrode maintained at suitable potential difference with respect to said discharging portions, while'the precipitating field is maintained between oppositely charged electrodes of extended area, preferably placed relatively close together as compared with the spacing between the discharge and collecting electrodes in ordinary electrical precipitation apparatus. Furthermore, these precipitating electrodes are preferably so formed as to substantially prevent or minimize electrical discharge therefrom at all positions within the precipitating field, and for this purpose the edges or ends of said electrodes may advantageously be rounded or curved so as to avoid sharp edges or corners. When electrodes of this? type areemployed in the precipitating field, not only may the spacing between electrodes be made relatively small, but also the relation of potential difference between said electrodes to distance therebetween may be increased consid- "erably above the limiting value of this relation when discharging electrodes are employed, so that the precipitating field strength may be made at least twice as great as in ordinary electric precipitation apparatus. Thus, it is possible to obtain a greatly increased precipitating force acting on the suspended particles and at the same time provide a relatively short average precipitating path for suchparticles, and the efliciency of precipitation may be materially increased.

The accompanying drawings illustrate apparatus in accordance with this invention, and referring thereto: i

Fig. 1 is a horizontal section of one form of such apparatus, on line l-l in Fig. 3.

Fig. 2 is a longitudinal vertical section thereof on line 2-4 in Fig. 1.

Fig. 3 is a transverse section on line 31-4 in Fig. 1.

Fig. 4 is a vertical section of another form of such apparatus, particularly adapted-for treatment of relatively small gas volumes.

Fig. 5 is a horizontal section on line 5-5 in Fig. 4.

Fig. 6 isa view similar to Fig. 4, showing another modification of the invention.

Fig.7 is a longtudinal vertical section of an- Fig. 9 is a vertical section of a form of apparatus in which the forward end of one of the pro-'- cipitating field electrodes is utilized as a discharge electrode means.

Fig. 10- is a horizontal section on line Ill-I0 in Fig. 9. 1

Fig. 11 is a vertical section of another form of apparatus of the type last mentioned.

Fig. 12 is a section on line I2 in Fig. 11.,

. Fig. 13 is avertical section of another modification of the apparatus of this same type.

Fig. 14 is a sectional view on line "-44 in Fig. 13.

, In the form of the invention shown in Figs. 1 to 3 inclusive, the precipitator housing I is provided with inlet means 2 at one end and outlet means 3 at the other end, so as to provide for passage of gas therethrough in the direction indicated by the arrows. Electrode means adapted to produce ionization are disposed within a portion A of said housing adjacent the inlet end thereof, so as to maintain a charging field in this portion of the precipitator, while precipitating electrode means are disposed within a portion B of the precipitator housing, beyond the portion A, for maintaining a substantially non-discharging precipitating field in said last-mentioned portion of the precipitator.

.The charging field electrode means are shown as comprising discharge electrode elements 5, consisting for example of vertically extending wires, rods or other linear members of small diameter,

spaced sufliciently from one another to facilitate corona or brush discharge therefrom, and opposing electrode members 6 consisting for example of plates, screens, or other members of extended area. The discharge electrode members 5 are shown as mounted on supporting frame means I supported from transverse supporting members 8 resting on insulating supports 9, while the opposing electrode members 6 may be mounted on supporting frame members ll connected directly to the precipitator housing which may be electrically grounded as indicated at 12.

The precipitating electrodes are shown as comprising two sets of electrode members H and I5 respectively all of which are of extendedarea and are shown as consistingof hollow plate-like members having their ends or edge portions rounded said ends or edgeportions are disposed opposite to one another, so as to prevent or minimize elec-- trical discharge therefrom. ,The electrode elements M are shown as extending vertically above and below the upper and lower-edges of the elements l5, and connected to supporting frame members i! which are in turn supported upon the precipitator housing. The electrode elements IS, on the other hand, are shown as extendi longtudinally in both directions beyond the forward and rear edges of the elements I4, and connected to supporting frame members I! suspended from transverse supporting members H- which rest on insulating supports ii.

The source of electric current is shown as comprising a step-up transformer 23, and the full voltage of the secondary winding of said trans.- iormer is impressed upon the electrode means in the charging field A. For this purpose, one end of said secondary winding is indicated'as being connected by wire 24 to the grounded electrodes 6, while the other end of said secondary winding is connected to the discharge electrode members 5 as shown diagrammatically at 25. The precipitating electrodes II and I5 are shown as spaced considerably closer together than the electrode members 4 and 6, so as to provide a relatively short distance therebetween, and a suitable voltage is also impressed upon electrodes l4 and IS. The electrodes ll are in electrical connection with the grounded housing I and thence with the conductor 24 connected to one end of the transformer secondary winding, while the electrode elements ii are diagrammatically shown as connected by wire 26 to an intermediate tap on said secondary While the total potential difl'erence between the electrode members I4 and I5 may be somewhat less than the potential difference between the electrode members 5 and 6, it may be seen that the closer spacing of the electrode members I! and I5 permits a relatively high electrical field. intensity to be maintained therebetween. In general, the relation of potential difference to distance, between electrodes and I5, is preferably maintained higher than the maximum possible relation of potential difference to distance, between electrodes 5 and 8. It is not essential, of course, that the total impressed potential between the precipitating electrodes be less than that between the ionization electrodes,

and in some cases it may be equal thereto,- or greater.

In the operation of this formof apparatus, the gascontaining suspended particles passes first through the charging field A, wherein the suspended particles are charged by the ionization produced adjacent th'e'discharge electrode members5. It will be understood that some precipitation may occur in this field, but the velocity of "to the force of the precipitating field of relatively high intensity, and are driven toward,.and collected upon, the surfaces of one or the other of V the sets of electrode members I4 and I5, whence they may either fall by gravity or be remdved in any suitable manner, and caught in suitable collecting means at the bottom of the precipitator housing. Due-to the relatively close spacing of the electrodes II and 15, it will be seen that the maximum path through which any charged suspended particles must pass, in a direction transverse to the gas flow, in order to reach the surface of one of the electrodes M or I5, is relatively short, and since the electrical field intensity be-' tween said electrodes is also high, being preferably greater than could be maintained if either of said electrodes were of the discharging type, without causing disruptive discharge, it may be seen that efiicient precipitation may be obtained even when an alternating electric field is employed, since the particles will be caused to travel through this relatively short path during one-half cycle, andwill thus be effectively precipitated instead of being merely driven back and forth between the electrodes as is-the case when an alternating electric field is employed with the relatively great distance between electrodes and the relatively low field intensity which are ordinarily employed in electrical precipitation apparatus now in common'use.

In the form.of apparatus shown in Figs. 4 and 5, the charging field electrodes are shown as comprising a vertically extending wire or rod 3| of small diameter and the lower portion 32a of a cylindrical tube 32, said electrode 3| being disposed axially within said' tube. The precipitating field electrodes are shown as comprising the up,- per portion 32b of said tube, and a cylindrical member 33 disposed axially thereof, 'andof somewhat smaller diameter than said tube but of considerably larger diameter than the discharging electrode 3|. In this case, the electrode members 3| and 33 may be'maintained at the same potential with respect ta tube 32, and member 3| is shown as suspended from the lower end of member 33. The upper and lower ends of the The electrodes 3| and 33 may be connected by conductor ll to one terminal, and tube 32 may be connected by conductor 42 to the other terminal, of a suitable source of high potential alternating current, such as the secondary winding of transformer l3. Tube 32 is also preferably grounded, as indicated at 44.

Theoperation of this form of the invention is substantially the same as above described, the

gas passing first through the ionization field between electrode members 3| and 32a, wherein the suspended particles are electrically charged,

and then through the precipitating field between electrode ;members 33 and 32b, wherein the charged particles are precipitated upon the surfaces 'of said electrodes.

In Fig. 4, the upper and lower portions 32d and32b of the tubular outer electrode are shown as being of equal diameter. However, due to the greater diameter of electrode member 33 than of electrodemember 3|, the distance between the precipitating field electrodes 33 and 32b is materially less than the distance between the ionization electrodes 3t and 32a. Forthis reason the .electrical field intensity, or the relation of potential difference to distance between electrodes,

is considerably greaterin the precipitating field.

than in the ionization field. While this tends to increase the rapidity of precipitation of the suspended particles, for the reasons above set forth, it also produces a corresponding increase in velocity of gas in the precipitating field. In cases where this increased velocity maybe found objectionable, due to;a tendency of the gas to pick up and carry along particles of material afterthe same have been precipitated on the electrodes, an apparatus such as shown in Fig. 6 may be employed. In this case the ionization electrodes 3| and 32a and the precipitating electrodes 33 and 321; are substantially the sani as shown in Fig. 4, with the exception that V the lower portion 32a of the tubular outer electrode 32 is of somewhat smaller diameter than the upper portion 32b, so that the cross-sectional area of the gas passage space is substan- 'tially the same in both portions, thus providing substantially the same gas velocity'in the precipitating field as in the ionization field.

The apparatus shown in Figs. 7 and 8 is also adapted to maintain the velocity of gas fiow substantially uniform in the ionization and precipitating fields. In this case the ionization electrodes 5 and 6' are substantially the same .as shown in Figs. 1 and 2. The precipitating field electrodes I4 and I5 may also be substantially the same as shown in Figs. 1 and 2, but in this casev the electrodes l5 are shown as com prising .hollow cylindrical members'of sufi'icierft diameter to substantially prevent or minimize electrical discharge therefrom, it being understood that electrode members of this shape are substantially the equivalent of the plate-like electrode members of the type shown in Figs. 1

and 2. In this embodiment of the invention, the ionization field portion A of housing I is shown to be of considerably smaller width than the precipitating field portion B thereof, so that in spite of the great thickness of the electrode members l4 and I5 as compared to the electrode members 5' and 6., the effective cross-sectional areaof the free gas passage spaces is substantially the samein both portions. As before, the apparatus may be provided with an inlet connection 2' at one end and an outlet connection 3' at the'other end, so as to provide for passage of gas therethrough in such a direction as to pass first through the ionization field and then through the precipitating field. The operation of this form of apparatus is substantially the same as that shown in Figs. 1 to 3 inclusive, with the exception that the gas velocity is maintained substantially uniform in both the ionization field and the precipitating field. In this case, the electrical connections of the several electrode members to the source of electrical energy may besubstantially as shown in Fig. 1, although if desired, a somewhat greater voltage may be impressed between electrodes members l4' and I5 than between electrode members 5' and 6, so as to provide a greater 'field intensity in the precipitation field than in the ionization field.

In Figs. 9 and 10 there is shown a simple apparatus in which the necessity for providing separate discharging electrodes for maintaining the charging field is eliminated, by so forming the forward end portion of one of the precipitating field electrodes as to cause electrical discharge therefrom. This apparatus is shown as comprising a hollow cylindrical electrode member 4| 'of sufiicient'diameter to substantially prevent electrical discharge therefrom at the voltage to be of chamber 42 are uniformly spaced from one another and are of such configuration and relativeposition as to maintain a substantially nondischarging electrical field therebetween. A suitable electrical potential is maintained between said electrodes, electrode member 4| being shown as connected by conductor 45 to one terminal of the secondary winding of transformer 46, and the opposing electrode means 42 being connected by conductor 41 to the other terminal thereof and being preferably grounded as indicated at 48. Chamber 42 is provided with gas inlet means 49 at the lower end and gas outlet means 5| at the upper end.

The lower end of electrode member 4| is so formed as to cause electrical discharge therefrom. For this purpose said member is shown as tapering inwardly at its lower end to a sharp point 52. The wall of chamber 42 is preferably somewhat enlarged at the region opposite this dischargin point 52, being preferably formed as a part of aspherical electrode surface as indifrom said point at the potential which is to be maintained between the precipitating field electrodes.

In this form of apparatus; when the electric potential is applied, a corona discharge takes place from the discharging point 52 of electrode member 4|, toward the opposing electrode means 53 and 54, and the gas entering the chamber through inlet means 49 is subjected first to this discharge so as to cause charging of the particles. The gas and charged particles then pass upwardly through the annular space between the precipitating field electrodes 4| and 42, where a nondischarging field is maintained, and the charged particles are thereby precipitated on the surfaces of said electrodes. The clean gas being discharged through outlet means 5|.

In the form of apparatus shown in Figs. 11 and 12, the gas enters through inlet means 55, and flows past constricting baflle means 51 into an upper header 58- and thence downwardly through precipitating chamber 59 and is discharged through outlet means 6|. Within upper header 58 is provided a pervious auxiliary electrode member such as metallic screen 62 extending substantially horizontally above substantially the entire cross-sectional area of precipitating chamber 58 and insulated from the ground as by means of insulating supports 63. Within precipitating chamber 59 are provided two sets of precipitating field electrddes 64- and 65. One of these sets, such as electrodes 64; consists of a plurality of parallel vertical plates mounted directly on grounded supporting members 61 and 58 connected to the grounded housing '59, while the other set of electrodes such as electrodes 66 is shown as comprising a plurality of vertical plates disposed alternately between the respective plates 64 and equally spaced therefrom, and mounted on supporting members 89 resting on insulating supports 1|. Supporting members 69 may extend through suitable orifice members 12 in plates 64. The lower ends of plates 66 may be connected Am alternating electric potential is preferably maintained between the grounded electrode plates 64 and the auxiliary electrode 52. For example, the electrode plates 64 may, as shown, be connected by conductor 16 to one terminal of the secondary winding of transformer 11, which is also preferably grounded as indicated at 18, while theelectrode 62 may be connected by conductor 19 {to the other terminal of said secondary winding. An alternating electric potential is also preferably maintained between the respectiveelectrode plates 64 and 65. For this pmpose,

the insulated electrode plates 56 may be connected by conductor to a point, of suitable potential with respect to ground for example, to an intermediate tap of the transformer secondary wind- In thiscase the gas entering through inlet means 56 is directeddownwardly between bailie means 51 and passes through pervious electrode member 62 and is subjected first to the charging effect of the ionization field between the upper edges of the electrode members 54 and 05 and auxiliary electrode member 62, whereby the suspended particles are electrically charged. Upon passing downwardly between the oppositely charged electrodes 64 and 66, between which a substantially non-discharging field is maintained, the charged particles are precipitated upon the surfaces of said last-mentioned electrodes, while the clean gas is discharged through outletmeans 6|.

The form of apparatus shown in Figs. .13 an 14 is similar to that shown in Figs. 11 and 12,

with the exception that the pervious electrode member such as screen 62' is electrically grounded, while both of the sets of precipitating field.

electrode plates GI and 66" areinsulated with respect to ground potential. The electrode plates 64' are shown as mounted on supporting members 82 resting on insulating supports 83, while the electrode plates 66' are shown as mounted on supporting members 84 resting on-insulating supports 85. The edge portions of electrode plates 64' are cut away opposite the supporting members 84 of the other set of electrodes, as shown at 86, while the electrode plates 66 are similarly cut awayas indicated at 81, opposite the sup- 62' to provide. corona discharge from said edges V at the voltage employed, while the electrode mem:

bers 64' and 66 are preferably spaced closer together than the distance from said edges 93 to said electrode 62', so as to maintain a precipitating field I of high intensity therebetween. As shown, the electrode member 52" may in this case be mounted directly on the housing of the precipitator, which provides the electrical connection thereof to the grounded conductor 88.

The operation of this form of apparatus. is substantially the same as that described in connection with Figs. 11 and 12, the gases to be cleaned entering through inletmeans SG' at the top of the apparatus and passing downwardly,-

first through the ionization field between discharging edges 33 and auxiliary electrode means 62' and then through the precipitating field be tween electrode members 64' and 65, whereby the particles are precipitated upon the surfaces of the last-mentioned electrodes, and the clean gas.

being discharged through outlet means 61'.

What I claim is:

1. The method of electrical precipitation which comprises passing. gas containing suspended material through a charging field in which ionization is produced between opposing electrode means. and

cipitating field between oppositely charged electhen passingsaid gas through an alternating pretrode means both having extended surface, said electrode means in the precipitating field being 'spaced closer together than the electrode means in the charging field, and the potential difference therebetween being sufiicient to cause movement of charged particles across the space betweenthe electrode means in said precipitating field during, one-half cycle of said alternating field.

I 2. An apparatus for electrical precipitation comprising substantially non-discharging precipitating electrode means disposed opposite one another, means for maintaining an electrical potential between said electrode means, means for passing gas between said electrode means,;the forward end of at least one of said precipitating field electrode means being so formed as to promote electrical discharge therefrom, auxiliary electrode means disposed opposite said forward end of said precipitating field electrode means and insulated from both of said precipitating electrode means, and means for maintaining an electric potential between said auxiliary electrode means and said forward end portion of said precipitating field V I electrode means independently of said first-named electrical potential. y

3. An apparatus as set forth in claim 2, in which the spacing of said precipitating electrode means from one another is materially less than the spacing of said auxiliary electrode means from said forward end portion of said precipitating field electrode means.

4. An apparatus for electrical precipitation comprising housing means provided with inlet and outlet means, precipitating field electrode means disposed within said housing and having extended surfaces disposed opposite one another, at least one of said electrode means being provided with discharging edge portions at the end toward said inlet means, means for maintaining an electrical potential between said precipitating electrode means sufficient to provide a precipitating field of high intensity therebetween but insuificient to cause material electrical discharge therebetween, auxiliary electrode means disposed between said inlet means and said discharging edgeportions of said precipitating electrode means and means for maintaining a separate electrical potential between said auxiliary electrode means and said discharging edge portions surficient to produce electrical discharge from said portions.

5. An apparatus for electrical precipitation comprising housing means provided with inlet and outlet means, precipitating electrode means disposed within said housing and having extended surfaces opposite one another, at least one of said electrode means being provided with discharging edge portions at the end toward said inlet means, pervious auxiliary electrode means disposed between said inlet means and-said discharging edge portions of the precipitating electrode means in such position as to cause gas to pass through said.

pervious electrode means in passing from said inlet means toward said precipitating electrode means, and electric power supply means connect- .ed to said precipitating electrode means and said auxiliary electrode means and adapted to maintain an electrical potential between said precipitating electrode means sufiicient to provide a precipitating field of high intensity therebetween but insuificient' to cause material electrical discharge therebetween and to maintain an electricalpotential between said discharging edge portions and said auxiliary electrode means sufiicient to produce electrical discharge from. said edge portions.

6. The method of electrical precipitation which comprises passing gas containing suspended material through a charging field in which ionization is produced between opposing electrode means, and then passing said gas through an alternating precipitating field between oppositely charged electrode means both'having extended surface, said'electrode means in the precipitating field be- 6 I ing spaced closer together than the electrode means in the charging field, and the potential difference therebetween being suflicient to cause.

movement of charged particles across the space 6 between the electrode means in said precipitating field during one-halt cycle 01 said alternating field, said alternating electrical potential being greater than the maximum alternating potential which could be applied between said precipitating electrodes if either of said electrodes were formed as a discharging electrode.

WALTHER DEUTSCH. 

